Production of biomimetic artificial or electronic skin requires large-scale sensor arrays that are capable of sensing pressure, humidity and temperature with high resolution and low response times. These sensor arrays, designed to provide physical and chemical information of the environment can be utilized by a variety of applications such as medical prosthesis and robotics industries. For example, prosthetic limbs can be covered with artificial or electronic skin to provide the user with a sense of touch in the form of different pressure levels, and robotic limbs can be integrated with artificial or electronic skin surface of varying sensitivities to allow autonomous control for handling objects. Robotic surgeries, health monitoring and many other potential applications, can benefit from the use of artificial or electronic skin having varying sensitivities to pressure, temperature, and/or humidity conditions (Eltaib et al., Mechatronics 2003, 13, 1163-1177; Lee et al., Mechatronics 1999, 9, 1-31; and Dargahi et al., Int. J. Med. Rob. Comp. Ass. Surg. 2004, 1, 23-35).
Flexible sensors, originally designed as soft and rubbery components of hand-held consumer electronics and displays, are now being explored for use as ultrathin health-monitoring tapes that could be mounted onto the skin (Tiwana et al., Sens. Actuat. A 2012, 179, 17-31; and Rogers et al., PNAS, 2009, 106, 10875-10876). Low-power touch-sensitive platforms of flexible sensors that are based on nanowires, carbon nanotubes, nanoparticles, rubber dielectric layers, and organic field-effect transistors, have been successfully demonstrated (Takci et al., Nature Mater. 2010, 9, 821-826; Herrmann et al., Appl. Phys. Lett. 2007, 91, 183105; Siffalovic et al., Nanotech. 2010, 21, 385702; Vossmeyer et al., Adv. Funct. Mater. 2008, 18, 1611-1616; Maheshwari et al., Science, 2006, 312, 1501-1504; Mannsfeld et al., Nature Mater. 2010, 9, 859-864; Pang et al., Nature Mater. 2012, 11, 795-801; Matsuzaki et al., Sens. Actuat. A 2008, 148, 1-9; Lacour et al., Annual International Conference of the IEEE on Engineering in Medicine and Biology Society (EMBC), 2011, 8373-8376; Someya et al., PNAS 2004, 101, 9966-9970; Cosseddu et al., IEEE Elec. Dev. Lett. 2012, 33, 113-115; Joseph et al., J. Phys. Chem. C 2008, 112, 12507-12514; Boland, J. Nat. Mater. 2010, 9, 790-792; and Yu-Jen et al., IEEE Elec. Dev. Lett. 2011, 58, 910-917).
US 2011/0019373 discloses an arrangement for sensing ambient conditions in electric equipment and/or for sensing biometric variables of a user, preferably applied in mobile terminals.
US 2012/0062245 discloses an apparatus comprising: a dielectric structure including a plurality of elastomeric regions separated from one another by space regions, the elastomeric regions being configured and arranged. in response to pressure, to compress and thereby exhibit a changed effective dielectric constant corresponding to a state of compression of the elastomeric regions; and a sense circuit including a plurality of impedance-based sensors, each impedance-based sensor including a portion of the dielectric structure and configured and arranged to respond to the change in dielectric constant by providing an indication of the pressure applied to the dielectric structure adjacent each sensor.
In order to achieve wide range implementation of flexible sensors as artificial or electronic skin, several requirements have to be met. First, these sensors need to afford a wide dynamic range that will enable measuring both low pressures (i.e. 1-10 KPa) for small object manipulation as well as high pressures (i.e. 10-100 KPa) for manipulating heavy objects. Second, these sensors require the simultaneous. measurement of pressure (touch), humidity, temperature and/or the presence of chemical compounds (Arregui et al., IEEE Sensors J. 2002, 2, 482-487; Cook et al., JPMC 2009, 5, 277-298; Shunfeng et al., IEEE Sensors J. 2012, 10, 856-862; Lopez-Higuera et al., J. Lightwave Tech. 2011, 29, 587-608; Konvalina et al., ACS Appl. Mater. Interf. 2012, 4, 317-325; Bay et al., J. S. Rob. Autom. Mag. IEEE 1995, 2, 36-43; and Wang et al., Langmuir 2010, 26, 618-632). Additional requirements include low-voltage/low power operation (typically below 5V), to be compatible with commonly used batteries of portable devices (Tsung-Ching et al., J. Disp. Tech. 2009, 5, 206-215). Finally, these sensors require easier, faster, and more cost-effective fabrication techniques to afford their wide application.
Layers of metallic-capped nanoparticles (MCNPs) on flexible substrates are potential candidates for a new generation of highly sensitive flexible sensors that meet these requirements (Herrmann et al., Appl. Phys. Lett. 2007, 91, 183105; Wang et al., Langmuir 2010, 26, 618-632; Wuelfing et al., J. Phys. Chem. B 2002, 106, 3139-3145; Haick, J. Phys. D 2007, 40, 7173-7186; Tisch et al., MRS Bull. 2010, 35, 797-803; Tisch et al., Rev. Chem. Eng. 2010, 26, 171-179; Vossmeyer et al., Adv. Funct. Mater. 2008, 18, 1611-1616; Farcau et al., J. Phys. Chem. C. 2011, 115, 14494-14499; and Farcau et al., ACS Nano 2011, 5, 7137-7143). The electrical properties of MCNP films exponentially depend on the inter-particle distance. Thus, deposition of the MCNPs on a flexible substrate allows modulating the resistance either by stretching or by bending the substrate. Geometry and mechanical properties of the substrate also affect the inter-particle separation. For example, metal-enhanced fluorescence, optical properties, and small-angle X-ray spectroscopy (SAXS) studies have shown that the nanoparticle separation depends on the substrate strain. Moreover, theoretical calculations have shown that the sensitivity of individual sensors to tactile load can be adjusted by controlling the thickness of the substrate.
WO 2009/066293, WO 2009/118739, WO 2010/079490, WO 2011/148371, WO 2012/023138, US 2012/0245434, US 2012/0245854, and US 2013/0034910 to some of the inventors of the present invention disclose apparatuses based on nanoparticle conductive cores capped with an organic coating for detecting volatile and non-volatile compounds, particularly for diagnosis of various diseases and disorders.
There remains an unmet need for the combined sensing of pressure, temperatures and humidity for multi-functional electronic or artificial skin applications.